The present invention relates to a tandem mill suitable for control of the sectional profile and shape of rolled articles.
A cold or hot tandem mill generally comprises serially arranged four to seven stands of common four-high mills (hereinafter called rolling mill N) including work rolls and back-up rolls and, preferably, roll benders. Recently, there has been a growing demand from users for steel sheets of high quality, particularly for such sheets having uniform thickness distribution in the lateral direction (that is, free from sheet crown and edge drop) and good flatness.
In a conventional tandem mill in which the roll crown of each stand is varied according to variation in the width, thickness and quality of the material which was rolled by using roll bending effectively, it has been impossible to obtain the desired flatness since there were provided too many kinds of initial crown of the work rolls which necessitated too frequent exchange of rolls, resulting in decrease in production efficiency.
While roll bending has been fairly effective, the conventional roll bending method has a limit to the ability for correcting and controlling the shape of material to be rolled and has not been sufficiently effective particularly in the case where the variation in rolling width is large.
As a method for improving the ability to control the sectional profile and the shape, the technical idea of providing the back-up roll of the tandem mill with steps has been proposed. This stepped back-up roll has a flat central portion and tapered ends, and the flat central portion is somewhat smaller in width than the material to be rolled. The back-up roll was provided with the steps firstly for minimizing the bending in the work roll by the rolling load and secondly for increasing the correcting ability due to the roll bending. The stepped back-up roll, however, has a disadvantage that each change in the sheet width requires an exchange of rolls according to the sheet width, which thereby decreases the productivity and increases the number of reverse rolls required. Accordingly, there have been developed various back-up rolls requiring no exchange of rolls even for changes in the sheet width and yet which are capable of providing the same effects as the stepped back-up rolls.
One of such rolling mills is a sliding expandable sleeve mill (hereinafter called rolling mill A) in which the expandable sleeve of the sleeve roll is slidable in the direction of the roll axis. An example of the rolling mill A is shown in FIG. 1. The rolling mill A is characterized in that a sleeve 3 is fitted onto each of back-up rolls 4 and the sleeve 3 is movable in the direction of the roll axis by a hydraulic cylinder 7. For movement of the sleeve 3 in the direction of the width of a material 2 to be rolled, a pressure medium is supplied from a medium passage 6 to a pressure acting groove 5 to release the force in the sleeve 3 holding it to the roll 4 to thereby facilitate the movement of the sleeve 3. The rolling mill A is preferably provided with a roll bender.
A further example is an intermediate back-up roll shifting mill (hereinafter called rolling mill B) which is a six-high mill having intermediate back-up rolls movable in the direction of the roll axis. The rolling mill B incorporates a pair of intermediate back-up rolls 10 between a pair of upper and lower work rolls 8 and a pair of back-up rolls 11, respectively, as shown in FIG. 2. The intermediate back-up rolls 10 are adjustably movable in the direction of the roll axis by driving couplers 12 according to the amount of variation of the sheet width of the material 2 to be rolled.
A still further example is an expandable fixed sleeve mill (hereinafter called rolling mill C) in which back-up rolls (variable crown, or VC, rolls) are radially expandable. The rolling mill C has a construction in which, as shown in FIG. 3, a sleeve 3 is fitted onto each of back-up rolls 4 and a pressure medium is supplied through medium passage 6 to a pressure chamber 5a defined between the roll 4 and the sleeve 3 to adjust the pressure of the medium, to thereby control the amount of the radial expansion of the sleeve 3. While FIG. 3 shows the VC roll having only one pressure chamber, a VC roll having two or more pressure chambers may, of course, be used if required.
The rolling mills described above have their respective characteristic features and each of them has effects in reducing sheet crown and edge drop and high ability to control the shape. While the rolling mills A and B have a noticeable shape control effect for any sheet width, it will be too costly to provide one of these rolling mills at every stand. On the other hand, while the rolling mill C is somewhat less adaptive than the rolling mills A or B to sheet width, it can be manufactured at a lower cost and yet is higher in response speed.
Further, in remodeling a conventional rolling mill N, while rolling mills A and C are relatively easily formed from the mill N, a rolling mill B requires much engineering work such as housing grinding and closure of the mill operation during such work.
Accordingly, an object of the present invention is to provide a tandem mill which has a low cost and excellent performance, by suitably incorporating the above-described rolling mills A, B, C, and/or N in a tandem mill.